1. Field of the Invention
The present invention relates to a content distribution/browsing system, a content distribution apparatus, a content browsing apparatus and a program enabling the contents to be browsed in the order intended by, for example, a content producer or a content browser.
2. Description of the Related Art
In the conventional field of content distribution, a superdistribution system is known as a method of prohibiting the browsing of a content item by other than the users who have purchased the content.
Various methods for the superdistribution system have been proposed. Basically, in each method for the superdistribution system, an encrypted content is distributed freely on the one hand and only the users who have purchased the encryption key of the encrypted content can browse the encrypted content on the other hand.
The persons who can browse the content are limited, for example, by encrypting the encryption key of the content with a public key or by encrypting the content with a symmetric key shared by the users. A method is also available in which the symmetric key is shared by a secret sharing scheme (for example, see Jpn. Pat. Appln. KOKAI Publication No. 2004-32307). The secret sharing scheme is described, for example, in A. Shamir: “How to share a secret”, Communications of the ACM, 22, 11, pp. 612-613 (1979).
The content distribution methods described above normally pose no problem. The study by the present inventor, however, shows that it is difficult to browse the content in the order intended by the content producer or content distributor. According to the intended order, the encryption keys for the content items of, for example, a plurality of stories including the first, middle and the last parts of a serial drama are distributed one by one from the first story.
Also, in browsing a plurality of content items, it is difficult to browse only a specified content item. In the case where an encryption key for a given number of content items are acquired, for example, it is difficult to permit a specified content item such as “a making video” to be browsed as a privilege.